1. Field of the Invention
The present invention relates to a current source inverter for changing DC power into three-phase AC power, and particularly, to a technique of safely and surely stopping the current source inverter when an abnormality occurs.
2. Description of the Related Art
Power inversion apparatuses for changing DC power into AC power are used for motor driving inverters, uninterrupted power sources, power factor correction circuits, and the like. The power inversion apparatuses are generally classified into voltage source (voltage-type) inverters having a DC link unit provided with a smoothing capacitor and current source (current-type) inverters having a DC link unit provided with a smoothing reactor.
FIG. 1 is a circuit diagram illustrating an example of the current source inverter according to a related art. In FIG. 1, a positive pole of a DC power source 1 is connected through a smoothing reactor 2 to a positive DC terminal 4 and a negative pole of the DC power source 1 is connected to a negative DC terminal 5.
An AC load 3 is a three-phase load having three AC terminals 6, 7, and 8. Connected between the positive DC terminal 4 and the AC terminal 6 is a series circuit including an insulated gate bipolar transistor (IGBT) Q1 and a diode D1. Connected between the positive DC terminal 4 and the AC terminal 7 is a series circuit including an IGBT Q2 and a diode D2. Connected between the positive DC terminal 4 and the AC terminal 8 is a series circuit including an IGBT Q3 and a diode D3.
Connected between the negative DC terminal 5 and the AC terminal 6 is a series circuit including an IGBT Q4 and a diode D4. Connected between the negative DC terminal 5 and the AC terminal 7 is a series circuit including an IGBT Q5 and a diode D5. Connected between the negative DC terminal 5 and the AC terminal 8 is a series circuit including an IGBT Q6 and a diode D6.
Gate drivers 11 to 16 are arranged for the IGBTs Q1 to Q6, respectively. Each of the gate drivers 11 to 16 is connected between a gate and an emitter of the corresponding IGBT, to apply a gate signal to the IGBT and thereby turn on the same.
Operation of the current source inverter of FIG. 1 will be explained. When the gate driver 11 (12 to 16) applies a gate signal of, for example, +15 V between the gate and emitter of the IGBT Q1 (Q2 to Q6), the IGBT turns on. When the gate driver 11 (12 to 16) applies a gate signal of, for example, 0 V or a negative voltage between the gate and emitter of the IGBT Q1 (Q2 to Q6), the IGBT turns off.
Based on control signals (3-phase, 120-degree conduction system) from a control circuit (not illustrated), the gate drivers 11 to 16 turn on/off the IGBTs Q1 to Q6, thereby supplying a required current to the AC load 3.
More precisely, the IGBTs Q1 and Q5 turn on at certain time (0-degree phase), to pass a current from the AC terminal 6 to the AC load 3 and to the AC terminal 7. At 60-degree phase, the IGBTs Q1 and Q6 turn on to supply a current from the AC terminal 6 to the AC load 3 and to the AC terminal 8.
At 120-degree phase, the IGBTs Q2 and Q6 turn on to supply a current from the AC terminal 7 to the AC load 3 and to the AC terminal 8. At 180-degree phase, the IGBTs Q2 and Q4 turn on to supply a current from the AC terminal 7 to the AC load 3 and to the AC terminal 6.
At 240-degree phase, the IGBTs Q3 and Q4 turn on to supply a current from the AC terminal 8 to the AC load 3 and to the AC terminal 6. At 300-degree phase, the IGBTs Q3 and Q5 turn on to supply a current from the AC terminal 8 to the AC load 3 and to the AC terminal 7.
Another related art described in Japanese Unexamined Patent Application Publication No. H05-236756 discloses a protection apparatus for a current source inverter.
According to this related art, the current source inverter has a rectifying unit to rectify power from an AC power source, an inverting unit to change a direct current outputted from the rectifying unit into a high-frequency alternating current, a DC reactor connected between the inverting unit and the rectifying unit, to smooth DC ripple components, and a load to receive the high-frequency alternating current from the inverting unit. In the current source inverter, the load is a parallel resonant circuit and the inverting unit employs self-turn-off elements. Each arm of the rectifying unit is a series circuit including a self-turn-off element and a diode. Between a positive pole and a negative pole on the output side of the rectifying unit, a diode is connected with a cathode thereof connected to the positive pole and an anode to the negative pole.
With the use of the self-turn-off elements for the rectifying unit, this related art stops a current to the DC reactor simultaneously with a blockage of gates. The diode connected to the output of the rectifying unit forms a flywheel circuit to reduce an overcurrent duty of the self-turn-off elements in the inverting unit.